This invention relates to a tubular handling device. More particularly, but not be way of limitation, this invention relates to a tubular slip device and method.
In the drilling for oil and gas, the tubular members utilized during drilling, completion and work over operations are required to be hung off at the drill floor. The device generally used is referred to as a rotary slip. The prior art devices include an apparatus capable of encircling the tubular member. The apparatus has on its inner face slip means for gripping onto the tubular member. The apparatus is placed into a slip bowl on the drill rig floor, as is very well understood by those of ordinary skill in the art. Conventional rotary slips are commercially available from Access Oil Tools, Inc. of New Iberia, La. under the name “DU” and “SDU” Style Rotary Slips.
In the normal operation of rotary slips, the weight of the pipe tends to wedge the three slip segments back latterly into the slip bowl. The teeth like projections of the inserts dig into the pipe then the slip wedges into the bowl to prevent the pipe from falling into the hole while making or breaking out connections on the rig floor. The bottom ledge of the slip segment, on which the bottom inserts sit, tends to carry a disproportionately large amount of the weight on the slip. Failure of a slip tends to manifest itself in bending or toeing outward of the bottom of the slip segments on this ledge, especially when the slips sit in a worn bowl since the slips are unsupported.
The slip device is inserted into a slip bowl on the drill floor. The slip device is constructed in a generally wedge shape and contains die inserts. The work string is disposed within the slip device and the slip device, and in particular, the die inserts will engage the work string. The inner section of the slip device will engage the work string which in turn cause the die inserts to the engage the work string.
The basic slip and bowl design is used for running drill pipe, casing, liners, bottom hole assemblies, etc. As the search for oil and gas continues, operators find it necessary to drill in more exotic environments, which includes ocean drilling. The water depths in ocean drilling may reach 10,000 feet and more in some instances. Thus, as operators run into the wells with casing, for instance, a landing string that is attached to the casing string. The landing string is necessary due to the 10,000 feet of riser in place which runs from the floating rig floor to the ocean floor. As will be appreciated, the combined landing string and casing applies a heavy load on the slip and bowl.
In combination with this deep water drilling, the actual wells that are drilled are increasingly deep in order to strike these commercially feasible hydrocarbon reservoirs. Hence, these wells can easily reach 25,000 feet in length. The equipment used with these deep water wells is large and extremely heavy. As understood by those of ordinary skill in the art, the lifting and lowering capacity of the drilling rigs is being severely tested.
For instance, if an operator is running a casing string into a well bore, the operator is required to lower that proper amount of casing. However, the operator will also be required to lower a landing string, and wherein the ultimate length of the landing string will be basically equal to the depth of the water. Therefore, the weight of the casing string and the landing string has pushed the operating capacity of the drilling rigs to its maximum.
The landing string is specifically designed to provide the very high tensile strengths to safely land out casing in the sub-sea well head. As the water depth increases, the length and weights of the landing string increase proportionateley. Existing mobile offshore drilling units (MODU's) are now operating at or near their maximum hoisting capabilities. Casing loads of 1,600,000 pounds have been experienced. This exposes the entire load hoisting system to maximum loading.
As the loads are increased, there is a danger of crushing the pipe, or alternatively, of slip failure. Conventional slips have a three inch (which translates to 7.12502 degrees) or four inch (which translates to 9.46232 degrees) taper per foot. This means for every twelve inches of vertical height at the top of the slip, the slip is three or four inches larger in diameter than the bottom. This is what helps to create the wedge effect in the bowl that suspends the pipe while connections or made to extend or shorten the drill string when going in or coming out of the hole. The prior art tapering worked well for a long time in the oilfield. However, with the use of landing strings in deepwater drilling and running long strings of casing down to the ocean floor on the bottom of a string of drill pipe, the crushing of the drill pipe, or alternatively, the slip failure has become an area of significant concern. In the case of failure, the damage to the well could be catastrophic and could lead to dire consequences for the rig crew.
Therefore, there is a need for a slip that will not crush the landing string. Also, there is a need for slips that will support heavy loads, including landing strings. Additionally, there is a need for slips that will grip these heavy tubulars, including landing strings.
There is also a need for a slip device that ensures that the total weight of the string is distributed more evenly over the full vertical height of all the slip segments. There is also a need for a rotary slip that can withstand significant loading forces without premature failure or fatigue. These needs, and many others, will be met by the invention herein disclosed.